Activation of micro, delta or kappa opioid receptors by DAMGO, DPDPE, U-50488 or U-69593 respectively causes antinociception in the formalin test in the naked mole-rat (Heterocephalus glaber).
Data available on the role of the opioid systems of the naked mole-rat in nociception is scanty and unique compared to that of other rodents. In the current study, the effect of DAMGO, DPDPE and U-50488 and U-69593 on formalin-induced (20 microl, 10%) nociception were investigated. Nociceptive-like behaviors were quantified by scoring in blocks of 5 min the total amount of time (s) the animal spent scratching/biting the injected paw in the early (0-5 min) and in the late (25-60 min) phase of the test. In both the early and late phases, administration of 1 or 5 mg/kg of DAMGO or DPDPE caused a naloxone-attenuated decrease in the mean scratching/biting time. U-50488 and U-69593 at all the doses tested did not significantly change the mean scratching/biting time in the early phase. However, in the late phase U-50488 or U-69593 at the highest doses tested (1 or 5 mg/kg or 0.025 or 0.05 mg/kg, respectively) caused a statistically significant and naloxone-attenuated decrease in the mean scratching/biting time. The data showed that mu, delta or kappa-selective opioids causes antinociception in the formalin test in this rodent, adding novel information on the role of opioid systems of the animal on pain regulation.
Towett
Philemon Kipkemoi
PK
Neurophysiology and Neuropharmacology Research Laboratory, Department of Veterinary Anatomy, University of Nairobi, P.O. Box 00100-30197, Nairobi, Kenya. towettp@yahoo.com
Kanui
Titus Ikusya
TI
Maloiy
Geoffrey Moriaso Ole
GM
Juma
Francis
F
Olongida Ole Miaron
Jacob
J
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology*; D018712:Analgesics, Non-Narcotic / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D044482:Benzeneacetamides / Q000494:pharmacology*; D003627:Data Interpretation, Statistical; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology*; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology*; D005557:Formaldehyde; D007274:Injections, Intraperitoneal; D008297:Male; D019577:Mole Rats; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010146:Pain / Q000139:chemically induced / Q000517:prevention & control*; D010147:Pain Measurement / Q000187:drug effects*; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D017465:Receptors, Opioid, delta / Q000819:agonists*; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D017450:Receptors, Opioid, mu / Q000819:agonists*
D018712:Analgesics, Non-Narcotic; D000701:Analgesics, Opioid; D044482:Benzeneacetamides; D009292:Narcotic Antagonists; D011759:Pyrrolidines; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D005557:Formaldehyde; D009270:Naloxone; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D020881:Enkephalin, D-Penicillamine (2,5)-; C045444:U 69593